A pulse counter serves many useful purposes. For example, in electronic systems, the need often arises to provide a reset signal when power is initially applied to the system. The reset signal is applied for a predetermined time interval of sufficient duration to assure stable operation of the system, and thereafter removed. For electronic systems containing a source of pulses, a power on reset apparatus may include a pulse counter which begins in a known state after power is applied, and provides an output signal corresponding to a power up reset signal until a predetermined count is reached.
A pulse counter may also be used as a frequency divider. The latter is accomplished by applying an output signal of the counter to reset the counter after counting a predetermined number of input pulses, equal to the division factor of the frequency divider.
In the prior art, a simple pulse counter may be realized using a diode, a resistor, and a capacitor in series. Each successive input pulse adds charge to the capacitor through the series diode until the voltage across the capacitor exceeds a predetermined threshold level. However, such prior art counter often requires a large value resistor and capacitor, both of which are difficult to accurately realize in integrated circuit form. Moreover, such prior art counter is frequency and amplitude dependent in that the input pulses must be substantially at a known predetermined frequency and at a known predetermined amplitude in order that the output indication represent a predetermined pulse count.